MicroRNA-31 is cell cycle-regulated

Non-coding RNAs (ncRNA) represent a considerable portion of the mammalian transcriptome and are involved in a variety of fundamental cellular processes like transcription, translation, dosage compensation and differentiation. MicroRNAs (miRNAs) are small ncRNAs and pleiotropic regulators of gene expression. Some are known to be aberrantly expressed in cancer and other diseases. In lung cancer miRNA-31 functions as oncogene and in breast cancer miRNA-31 acts as a tumour suppressor by decreasing the rate of metastasis. We found that miRNA-31 is significantly overexpressed in colon cancer compared to normal colon tissue. Furthermore, using the UCSC Genome Browser we could identify the non-coding RNA LOC554202 locus as gene host for the miRNA-31 gene. In order to understand the function of ncRNAs, one important line of investigation is to look at regulation of their expression. We observed that the LOC554202 ncRNA is differentially expressed during cell cycle. Its RNA level increases dramatically in the G₁ phase. Importantly, miRNA-31 is also differently expressed during the cell cycle. The expression level of miRNA-31 is at a maximum in S phase. Here we demonstrate for the first time a cell cycle-dependent expression of miRNA‑31. Furthermore, we identified the promoter region of LOC554202. In chromatin immunoprecipitation (ChIP) experiments we demonstrated that this promoter is responsive to the E2F cell cycle-transcription factor. Taken together, our findings suggest that miRNA-31 and LOC554202 are co-regulated during the cell cycle. These results provide new insights into the regulation of ncRNAs and could be of general importance to understand the mechanism by which miRNAs act in cancer or other diseases.